tallbridgeguy

So here is the FHWA’s webpage on Accelerated Bridge Construction. It is not a very impressive site. For one thing it shows a lot of outdated material and to me it doesn’t really seem serious about investing in ABC designs.

What do I mean by not serious, well, look at the page. Do you see any mention of new projects, help for State DOTs to develop new ABC directions or exciting news about design help. Nope, it plugs a conference from last March on the front page. When I visited the site today, it showed its last page update was seven months ago!

If the FHWA is really interested in ABC designs, why isn’t the page more vibrant? I doubt any business could afford to go seven months without adding something to their site.

One of the things I think can make a better project is the use of 3D visualizations. For example, most engineers can take a 2D drawing and construct a bridge. But 3D representations of the design can really help engineers and their clients understand what the project will look like before it is built.

ABC bridges probably need more visualizations than standard bridges because a small mistake in the design can become a very large mistake in the field.

To that end I have started a little visualization company called 3D Bridge Design. Bridge Concepts draw by an engineer who actually knows how to design bridges.

ABC Bridge

This is a precast pier cap we used for a county bridge. The pipe piles were concrete filled and the cap was tied into the system by filling the holes. The holes in in the cap were made using corrugated steel pipes. The only problem was supporting the whole thing while you waited for the concrete to cure. We did design it so you could place beams the next day.

ABC substructures are one of the more challenging areas of bridge design. Joints in substructures can be problematic (think water getting in and corroding the steel holding the thing together).

A major issue is how to tie piers to piles. Here is a link to the North Carolina’s Beaufort and Morehead Railroad Trestle Bridge, which used precast pier caps tied to preplaced pipe piles.  (say that 3 times)

This type of system used the speed of precast caps and then the conventional method of using concrete to tie the pier together. We used a similar system in our last two ABC projects.

Okay why the push to ABC bridges? Speed of course. The most common argument for ABC is the issue of building a bridge quickly which would  minimize the impact to drivers and local businesses.

This is a very strong argument. I have worked on traditional bridges that took up to a year to build. This can have a big impact on traffic patterns but typically its the businesses that are affected the most. Taking away access to businesses or reducing entrances can really disrupt the flow of traffic to a company. Drivers often avoid congested areas which means they avoid the businesses.

The irony is that disruption to drivers and businesses are considered in design but are not readily used in benefit/cost ratios for projects.  So…ABC projects often look more expensive than traditional projects because we can’t quantify the costs to drivers and local businesses.

I wonder what the one car knows....

I designed a steel bridge that took 3 years to build. It turned out pretty well but high water events and staging really slowed the project down. It would have been interesting to try and design ABC piers for this project….Keosauqua Bridge Link.

A 3D model of the Keosuaqua Pier.

Obviously ABC would be great for rapid replacement projects, but you would probably need to have the bridge already sitting on the shelf. This means of course standardized design which saves money but stifles creativity.

Scour poblems...

Here is a link to an older ABC paper (2006) by John Fowler. ABC paper. It contains a good overview of the ABC reasoning and has PICTURES! Couple that with the fact that it is from Canada (where I grew up) and you can’t go wrong.(what no mention of hockey?)

The new I35 bridge was built fairly quickly. I guess it qualifies as an ABC bridge because it was built faster than a “normal” bridge. So that begs the question, how much faster does the construction of a bridge have to be to qualify as accelerated construction?

New I-35 Bridge - Figg

One of the ABC projects I worked on used precast abutments and pier caps. It was a good project but the funny thing was that we did not impose time restrictions so the bridge took almost the normal amount of time to build.

We replaced a beautiful Marsh Arch bridge with a three span precast beam bridge.

Paper Here.